First question - what class of campsite did you book? Probably the most important factor in requesting a particular loop is that what you want actually exists.
For example, if you booked a full-hookup site - there aren't any full hookup loops close to the marina.
ETA... Oh and if you're in a cabin, I'm afraid none of those (that you can request) are particularly close to the marina either. Fort map
HERE. Cabin loops are 2100-2800